Test of the Anderson-Stuart model and correlation between free volume and the 'universal' conductivity in potassium silicate glasses

Following recent finding it is shown that using conductivity and molar volume in binary potassium silicate glasses (considering the same batches) there is a common cubic scaling relation between them due to increase in alkali content. Emphasis is placed on the application of Anderson-Stuart model to describe the variation of activation enthalpy for conduction EA with potassium concentration. In this analysis were considered experimental parameters, like shear modulus G and relative dielectric permittivity ɛ, in wide composition range (between 1.7 and 40 K2O mol%). The effects of G, ɛ and free volume are taken into account. The drastic drop in conductivity up to 17 orders of magnitude for so many ion-conducting binary alkali silicate glasses is then mainly caused by the structure and the ion content. In particular, it is suggested that the glass network expansion, which is related to the available free volume, is a parameter that could explain the increase in ionic conductivity for this binary system.